The government has been quick to link the recent cases of mental health patients killing people with its attempt to push ahead with a reform of the law.

Fear of the mentally ill reached a new nadir when the cases of John Barrett and Peter Bryan hit the headlines in the last month.

Mr Barrett stabbed a cyclist to death in a south west London park less than 24 hours after walking out of a mental health hospital.

Mr Bryan's case is perhaps more notorious after he ate the brains of one of his two victims.

The Department of Health has defended the draft Mental Health Bill - which proposes allowing compulsory detention of people with severe personality disorder even if they have not committed an offence - against criticisms by MPs and peers by citing the recent cases.

Detention

The joint House of Commons and House of Lords Committee warned the bill made it too easy to lock people up and could lead to patients with only mild conditions being detained.

But a Department of Health spokeswoman said: "The tragic events of the last few weeks have shown that legislation has to strike a balance between protecting the rights of society with the rights of individuals."

However, campaigners claim initial conclusions about the two cases - both are subject to official investigations - suggest the draft Bill would have had little effect.

It is hard to see how the current draft bill would have made a difference in the cases of Bryan and Barrett

Both men had been treated for schizophrenia and as such could have been detained under the 1983 Mental Health Act.

Instead, they were allowed a degree of freedom - Mr Bryan was staying in an open psychiatric ward and Mr Barrett was only an informal patient - from the mental health hospitals where they were being treated.

Paul Farmer, chairman of the Mental Health Alliance, which represents 50 of the largest mental health groups, said the bill - first published in 2002 - had been driven by the case of Michael Stone, who killed Lin Russell and her daughter in a hammer attack in 1996.

Former Home Secretary Jack Straw believed a loophole in the law, which assumed people with severe personality disorders were untreatable and, therefore, could not be detained, had led to Stone being free to kill.

Inquiry

Mr Farmer said: "It is hard to see how the current draft Bill would have made a difference in the cases of Bryan and Barrett.

"Investigations are being carried out, but I think our clearest guide is from past inquiries which have tended to show that homicides happened, not because of inherent flaws in the law, but because of things that went wrong with the risk assessment."

He said despite recent investment by the government, mental health was still significantly under-funded.

In particular, London - where both the Barrett and Bryan cases happened - had severe problems with use of locum staff, meaning there was a lack of continuity of care, he said.

Peter Bryan ate the brains of one of his victims

"It is in this type of situation where mistakes are more likely to happen."

Andy Bell, of the Sainsbury Centre for Mental Health, said cases of mental health killings were often a case of the law not being interpreted correctly.

He also said we should be cautious about blaming care in the community.

"Between 30 and 50 killings each year out of 800 are by people who are in contact with mental health services.

"That has remained constant for years - before and after care in the community came in."

Sandra Gidley, a Liberal Democrats health spokeswoman, also agreed the current law should have protected the public in the recent cases.

"In those cases there was a known problem and it was not dealt with properly.

"We already have the means to deal with that problem and the system fell down."

However, Professor Peter Kinderman, chairman of the British Psychological Society's Mental Health Bill working party, said he could understand why the government was suggesting the Bill might have made a difference.

"It is right to say the recent cases were patients being treated with schizophrenia, and that is different from severe personality disorder, which the bill is primarily focused on.

"But the Bill does proposes changes to treatment in the community, making it easier to detain people.

"Saying that, the government must be very careful linking the two, they are very different and need to be treated differently."